Dependence of multiple climate states on ocean mixing parameters
Bibliographic record
Abstract
Multiple equilibria of the climate system, inferred from paleo reconstructions, have also been observed in both ocean‐only and coupled ocean‐atmosphere general circulation models. These multiple states are thought to be associated with different modes of operation of the meridional overturning circulation in the North Atlantic. It has recently been suggested that the stability of these states depends on the amount of vertical mixing in ocean models. Here we investigate the dependence of the hysteresis behaviour of the thermohaline circulation to sub‐gridscale mixing processes in the ocean. Using a simplified coupled ocean‐atmosphere model we find that both vertical and horizontal diffusivities have considerable influence on the stability of the different circulation modes. They also change the transition points from one circulation pattern to another. Larger vertical diffusivities lead to higher values of additional precipitation into the North Atlantic being necessary to stop the formation of deep water. However, for slightly increased evaporation, the state without deep water formation becomes increasingly unstable for stronger vertical diffusion. Larger values of horizontal mixing lead to a narrowing of the phase space for which two equilibria are stable. These results suggest that it is currently not possible, given the large uncertainty in ocean mixing, to quantitatively determine possible thresholds for the transition of the North Atlantic thermohaline circulation between on and off modes. This presents a policy predicament as it makes it extremely difficult to assign a probability for the future occurence of such nonlinear climate transition.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.008 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".